The present invention relates to a method of manufacturing a solar battery and, more particularly, to a method of manufacturing a solar battery employing a cell sealing film.
Solar cells which directly convert sunlight to electric energy are effective utilization of natural resources and prevention against environmental pollution.
A solar battery comprises, as shown in FIG. 2, a glass substrate 11 as a front-side transparent protective member, a back-side protective member (backside covering member) 12, ethylene-vinyl acetate copolymer (EVA) resin films 13A, 13B as sealing layers arranged between the glass substrate 11 and the back-side protective member 12, and solar cells such as silicon photovoltaic elements 14 sealed by the EVA resin films 13A, 13B.
To manufacture this solar battery, the glass substrate 11, the sealing EVA resin film 13A, silicone photovoltaic elements 14, the sealing EVA resin film 13B and the backside covering member 12 are successively overlaid in this order and integrated together by heating and pressurizing the EVA by virtue of the crosslinking of the EVA.
The sealing EVA resin films 13A, 13B are generally manufactured by means of a film forming method such as T-die extrusion or calendaring in which melt resin is extruded through a linear slit of an extruder die and is then quenched by a cooling roll or in a water quench bath.
As for adhesive films, an embossing treatment is sometimes applied to a formed film to provide a rough surface in order to improve the welding property and the contact bonding property.
Conventional sealing EVA resin films are not processed by the embossing treatment. Alternatively, even if processed by the embossing treatment, the depth of roughness formed by the embossing treatment is of the order of 5 xcexcm at the most. It should be noted that the thickness of a normal EVA resin film is several hundred xcexcm.
In the manufacture of a solar battery, since the EVA resin films are pressed against solar cells during the heating and pressurizing in the sealing integration process, some solar cells may be unfortunately broken due to this pressure. There is another problem that air is entrapped due to insufficient deaerating for the sealing integration and/or EVA resin film is deformed to flow out due to the heating and pressurizing and the resin may spew out of a side end of a laminated body, thus reducing the product yield.
It is an object of the present invention to provide a film for sealing a solar cell which can effectively prevent the solar cell from being damaged, prevent inferior deaeration, and prevent resin of the film from flowing out during the sealing integration process of manufacture of a solar battery, and which enables the manufacture of solar batteries with high product yield, and also to provide a method of manufacturing a solar battery using said layers for sealing solar cells.
A film for sealing a solar cell according to the present invention includes a film formed of ethylene-vinyl acetate copolymer resin. The film is processed by an embossing treatment to have concavities. A percentage P defined by the following equation is in a range from 5% to 80%;
P=VH/VAxc3x97100 (%) 
wherein VH is the total volume of said concavities per unit area of the film and VA is the apparent volume of the film which is the product of the maximum thickness of the film and the unit area.
The film for a sealing solar cell which is composed of a film processed by an embossing treatment to have the percentage (concavity ratio) P from 5% to 80% enables the manufacture of a solar battery with high product yield.